1. Field of the Invention
The present invention relates to a structure of a solar cell well suited for a power source of electric instrument with low power consumption, such as a calculator and a watch, and also relates to a method of fabricating the same.
2. Description of the Related Art
A solar cell is used as a sunlight electrical generating system, which is installed outdoors, or is used as a power source of an electric instrument with low power consumption, such as a calculator, a radio, and a watch. In the latter use, like a wrist watch, there is a case where importance is attached to not only the function but also to its external design. Accordingly, a mounting method of the solar cell is also devised, and it is directly used for a face of the watch, or is installed under a semitranslucent face of the watch to make it unnoticeable.
In most of solar cells used for electric instruments or the like, glass, stainless, organic resin material or the like is used for a substrate, and a photoelectric conversion layer is formed thereon with a thin film of amorphous semiconductor, microcrystalline semiconductor, or chalcopalide-based (or II-VI group) compound semiconductor. Especially, the solar cell using an organic resin material for the substrate is thin and lightweight, and has an excellent shock resistance so that it is not cracked even if it is dropped. Accordingly, it is suitable for mounting to a portable product, such as a card type calculator and a wrist watch. In the case where the solar cell is installed in a small electric instrument such as a wrist watch and a card type calculator, for the purpose of simplifying the layout of wiring lines, it is considered to be desirable that an external connection terminal is placed at a side opposite to a light incident surface of the solar cell.
There is a best known technique for forming a photoelectric conversion layer with a non-monocrystalline semiconductor material, such as amorphous silicon and microcrystalline silicon, fabricated by a plasma CVD method. As means for increasing the productivity of the solar cell and decreasing the manufacturing costs, there is known a method in which while a flexible substrate wound into a roll shape is rewound around another roll, respective unit operations such as film formation, printing, and laser working are carried out during the process by in-line processing to continuously make treatment. This method is called a roll-to-roll method.
In a non-monocrystalline semiconductor layer formed by the plasma CVD method, a substrate is heated to 100xc2x0 C. or more in view of the balance between acquisition of excellent photoelectric conversion characteristics and film formation speed. However, when an organic resin film of polyester or the like is heated, oligomer (polymer in which the repetition number of structural units is about 2 to 20) is apt to be produced. Further, since it is generally an equilibrium reaction, there is a tendency in that the amount is increased as the temperature is raised.
In a solar cell installed in an electric equipment, attention is paid also to its color tone, surface shape, and the like. Although a solar cell having a structure in which light is entered onto the solar cell through a substrate has a flat surface in its external appearance, surface reflection and a color tone at openings and portions between electrode patterns resulting from integrating working become different and conspicuous. Besides, oligomer deposited on the light incident surface has low adhesion force, and is apt to be dropped off. Therefore, it can be relatively easily removed. However, it pollutes the instrument incorporating the solar cell.
An object of the present invention is to provide a solar cell in which surface reflection is lowered, and a change of a color tone at openings and portions between electrode patterns resulting from integrating working is made inconspicuous, with the result that external appearance quality is improved.
In order to achieve the above-mentioned object, according to an aspect of the present invention, in a solar cell in which light is entered from a side of a translucent substrate, a transparent electrode layer, a photoelectric conversion layer, and a rear electrode layer are formed on one surface of a transparent organic resin substrate, a surface passivation layer made of an organic resin layer is formed on the other surface, and the surface passivation layer includes a filler.
In the solar cell, the surface passivation layer includes at least one selected from the group consisting of a white filler and a colorless filler.
In the solar cell, the surface passivation layer comprises at least one selected from the group consisting of phenoxy resin and thermally hardened resin of the phenoxy resin.
In the solar cell, nonaromatic isocyanate or melamine resin making a thermal crosslinking reaction with a hydroxyl group of the phenoxy resin is used as a crosslinking agent so as to thermally harden the phenoxy resin.
According to another aspect of the present invention, a solar cell includes a transparent electrode layer, a photoelectric conversion layer, and a rear electrode layer, which are formed on one surface of a transparent organic resin substrate, a first opening filled with an insulating resin and a second opening filled with a same conductive material as the rear electrode layer, which are formed in the transparent electrode layer and the photoelectric conversion layer, and a surface passivation layer made of an organic resin layer and formed on the other surface of the organic resin substrate, wherein the surface passivation layer includes a filler.
In the solar cell, the surface passivation layer includes at least one selected from the group consisting of a white filler and a colorless filler.
In the solar cell, the surface passivation layer comprises at least one selected from the group consisting of phenoxy resin and thermally hardened resin of the phenoxy resin.
In the solar cell, nonaromatic isocyanate or melamine resin making a thermal crosslinking reaction with a hydroxyl group of the phenoxy resin is used as a crosslinking agent so as to thermally harden the phenoxy resin.
The surface passivation layer having a main ingredient of phenoxy resin as disclosed in Japanese Patent Application Laid-open No. Hei 8-231675 and/or phenoxy resin added with nonaromatic functional isocyanate or melamine resin, is formed by a screen printing method or a roll coater method to obtain a thickness of 3 to 10 xcexcm. The surface passivation layer includes a filler, thereby forming irregularities of about 3 to 8 xcexcm, and gives an effect of lowering surface reflection.
According to still another aspect of the present invention, a method of fabricating a solar cell includes a first step of forming a transparent electrode layer on a transparent organic resin substrate, a second step of forming a photoelectric conversion layer on the transparent electrode layer, a third step of forming a first opening and a second opening reaching the substrate in the transparent electrode layer and the photoelectric conversion layer, a fourth step of forming an insulating layer covering the first opening and an upper end portion of the opening, a fifth step of forming a conductive layer covering the photoelectric conversion layer, the insulating layer, the second opening and an upper end portion of the opening, and a sixth step of forming a sealing resin layer on the photoelectric conversion layer and the conductive layer, the method further including a step of forming a surface passivation layer which may be carried out between any steps if they are subsequent to the second step.
In the method of fabricating the solar cell, the surface passivation layer includes a filler in addition to at least one selected from the group consisting of phenoxy resin and thermosetting phenoxy resin as a matrix resin component, and the surface passivation layer has a certain degree of an optical diffusibility in addition to an optical transparency.
In the method of fabricating the solar cell, nonaromatic isocyanate or melamine resin making a thermal crosslinking reaction with a hydroxyl group of the phenoxy resin is used as a crosslinking agent so as to thermally harden the phenoxy resin.
According to still another aspect of the present invention, a method of fabricating a solar cell includes a first step of forming a transparent electrode layer on a transparent organic resin substrate, a second step of forming a photoelectric conversion layer on the transparent electrode layer, a third step of forming a first conductive layer of a predetermined pattern on the photoelectric conversion layer, a fourth step of forming a first opening and a second opening reaching the substrate in the transparent electrode layer and the photoelectric conversion layer, a fifth step of forming an insulating layer covering the first opening and an upper end portion of the opening, a sixth step of forming a second conductive layer covering the photoelectric conversion layer, the insulating layer, the second opening and an upper end portion of the opening, and a seventh step of forming a sealing resin layer on the photoelectric conversion layer and the conductive layer, the method further including a step of forming a surface passivation layer after the second step.
In the method of fabricating the solar cell, the surface passivation layer includes a filler in addition to at least one selected from the group consisting of phenoxy resin and thermosetting phenoxy resin as a matrix resin component, and the surface passivation layer has a certain degree of an optical diffusibility in addition to an optical transparency.
In the method of fabricating the solar cell, nonaromatic isocyanate or melamine resin making a thermal crosslinking reaction with a hydroxyl group of the phenoxy resin is used as a crosslinking agent so as to thermally harden the phenoxy resin.